Piezoelectric ceramic transistor

ABSTRACT

A piezoelectric ceramic transistor is formed from a single-layered or multi-stacked layers piezoelectric ceramic voltage transformer and a capacitor, the capacitor being series connected to an input terminal of the piezoelectric ceramic voltage transformer to prevent electric power and prevent loss due to feedback, thereby compensating and increasing vibrations of the piezoelectric ceramic voltage transformer. Alternatively, the above connection scheme is achieved by either serial connecting a capacitor between a power output of the transformer and a load terminal, or parallel connecting a first capacitor to a power input of the transformer while a second capacitor is series connected between a power output of the transformer and the load terminal to obtain an increased power and thereby increasing the load current.

FIELD OF THE INVENTION

[0001] The invention relates to a piezoelectric ceramic transistor. Moreparticularly, the invention provides an electric element that issuitable for use in piezoelectric converter device, and can increaseelectric power.

BACKGROUND OF THE INVENTION

[0002] As shown in the schematic views of FIG. 1 and FIG. 2, presentdriving devices for driving cold cathode fluorescent lamp (CCFL)comprises a driving device and a CCFL driven by the driving device. Thedriving device comprises a power supply unit 1, a pulse width modulation(PWM) control unit 2, a driving unit 3, and a piezoelectric ceramicvoltage transformer 4′. The CCFL 7 connects to the PWM 2 through acurrent feedback 5 and the piezoelectric ceramic voltage transformer 4′connects to the PWM 2 through the voltage feedback 6. When this drivingdevice is turned on and inputs a voltage, the driving unit 3 immediatelydrives the piezoelectric ceramic voltage transformer 4′ that in turndrives the illumination of the CCFL 7 via piezoelectric ceramic reverseeffect. The PWM control unit 2 then detects the average output currentintensity of the CCFL 7 through current feedback 5 to output a resonancefrequency. The resonance frequency via the control unit 3and thepiezoelectric ceramic voltage transformer 4′ can control the averagecurrent of the CCFL 7. Hence, the light source generated from the CCFL 7is projected on the semi-transparent back panel to illuminate the backpanel and match the display frame of the LCD screen. Because theillumination of the CCFL 7 via driving of the above driving device islimited or uniform, several CCFL 7 are therefore needed to obtain auniform back panel illumination of the LCD screen. As a result, thefabrication cost is increased, and the fabrication process further isnot easily achieved.

SUMMARY OF THE INVENTION

[0003] It is therefore an object of the invention to provide apiezoelectric ceramic transistor that can overcome the above problems bybeing fabricated from a single-layered or multi-stacked layerspiezoelectric ceramic voltage transformer that has an input terminalseries connected to a capacitor. The above capacitor thereby forms abypass capacitor that increases the power and prevents a loss due tofeedback so that vibrations of the piezoelectric ceramic voltagetransformer are compensated. Alternatively, the above connection schemeis achieved by either serial connecting a capacitor between a poweroutput of the transformer and a load terminal, or parallel connecting afirst capacitor to a power input of the transformer while a secondcapacitor is series connected between a power output of the transformerand the load terminal to obtain an increased power and therebyincreasing the load current.

[0004] Another object of the invention is to provide a piezoelectricceramic transistor that is formed either via the connection oftraditionally known electric elements or via semiconductor packaginginto a single element.

[0005] Furthermore, another object of the invention is to provide apiezoelectric ceramic transistor that can reduce the number of CCFLmounted to the LCD screen so that the fabrication is facilitated and thefabrication cost reduced.

[0006] Still, another object of the invention is to provide apiezoelectric ceramic transistor that can allow CCFL with higher poweror of longer length, or CCFL drive with lower driving voltage.

[0007] To provide a further understanding of the invention, thefollowing detailed description illustrates embodiments and examples ofthe invention, this detailed description being provided only forillustration of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The drawings included herein provide a further understanding ofthe invention. A brief introduction of the drawings is as follows:

[0009]FIG. 1 is a block diagram illustrating a background light sourcedriving circuit of LCD screen;

[0010]FIG. 2 illustrates a corresponding circuit of the block diagram ofFIG. 1;

[0011]FIG. 3 is a block diagram of an implementation circuit accordingto an embodiment of the invention;

[0012]FIG. 4 is a circuit diagram corresponding to the block diagram ofFIG. 3;

[0013]FIG. 5 is a block diagram illustrating another embodiment of theinvention;

[0014]FIG. 6 is a block diagram still illustrating another embodiment ofthe invention;

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] Wherever possible in the following description, like referencenumerals will refer to like elements and parts unless otherwiseillustrated.

[0016] Referring to FIG. 3 and FIG. 4, two block diagrams schematicallyillustrate an implementation circuit according to an embodiment of theinvention. As illustrated, the piezoelectric ceramic transistor of theinvention is principally formed via serial connecting a capacitor to aninput terminal of a single-layered or multi-stacked layers piezoelectricceramic voltage transformer (piezoelectric layer). A LCD screen drivingdevice is illustrated as an example of embodiment of the invention. Thisdriving device comprises a power supply unit 1, a pulse width modulation(PWM) control unit 2, a driving unit 3, and a piezoelectric ceramictransistor 4. Constructed as above, the driving device is used to drivea cold cathode fluorescent lamp (CCFL) 7 that produces a light sourcefor the back-light of the LCD. The power supply unit 1 provides powernecessary for the operation of all the units of the driving device.

[0017] The PWM control unit 4 is connected to an input terminal of thedriving unit 3, and respectively receives a current feedback 5 from theCCFL 7 and a voltage feedback 6 from the piezoelectric ceramictransistor 4. From the current feedback 5 and according to the averagecurrent intensity detected from the output of the CCFL 7, the PWMcontrol unit 4 adequately controls the average current of the CCFL 7.

[0018] The driving unit 3 has an input connected to the PWM control unit2, and receives a resonance frequency outputted from the PWM controlunit 2.

[0019] The piezoelectric ceramic transistor 4 is formed by a capacitor42 parallel connected to an input terminal of a piezoelectric ceramictransformer 41. The capacitor 42 hence forms a bypass capacitor, whichallows to obtain a higher power. The capacitor 42 can prevent loss dueto feedback, and contributes to compensate the vibration of thepiezoelectric ceramic transistor 41.

[0020] When the driving device is turned on, the driving unit 3immediately drives the piezoelectric ceramic transistor 4 that in turndrives the CCFL 7 for illumination operation. At this moment, the PWMcontrol unit 2 measures the average current intensity outputted from theCCFL 7 through the current feedback 5, and outputs a resonancefrequency. The resonance frequency is delivered to the driving unit 3and piezoelectric ceramic transistor 4 to control the average current ofthe CCFL 7.

[0021] The examples of connection of the capacitor to the single-layeredor multi-stacked layers piezoelectric ceramic transformer areillustrated hereafter.

[0022] I. Single-Layered Piezoelectric Ceramic Transformer

[0023] A. Testing Conditions:

[0024] 1. V(DCV): 14V±5%

[0025] 2. load: lamp length 220 mm

[0026] 3. working frequency: 66 KHz±2 KHz

[0027] 4. light regulation conditions: DCV 0V

[0028] 5. single-layered piezoelectric ceramic transformer: 48 mm L×8 mmW×1.8 mm t

[0029] 6. static capacitance of low voltage terminal: 1.25 nf

[0030] 7. number of layers of input terminal: 1 layer

[0031] 8. testing temperature: 27±10%

[0032] B. Test Results:

[0033] Without capacitor: tube voltage (RMS) acV: 30V; tube current(AVG) InAacI: 0 mA;

[0034] With capacitor: tube voltage (RMS) acV: 567V; tube current (AVG)mAacI: 6.729 mA.

[0035] C. Testing Efficiency:

[0036] 1. without capacitor

[0037] tube voltage (RMS)acV×tube current (AVG)mAacI=P_out(w)

[0038] 30V×0 mA=0W

[0039] input voltage (DCV)×input current (DCI)=P_IN

[0040] 14V×0.036 A=0.5 W

[0041] 2. with parallel capacitor

[0042] tube voltage (RMS)acV×tube current (AVG)mAacI=P_out(w)

[0043] 576V×0.6729 mA=3.81 W

[0044] input voltage (DCV)×input current (DCI)=P_IN

[0045] 14V×1.268 A=17.72 W

[0046] As shown in the above test results, the addition of the capacitorof 0.127 uf can turn on the single-layered piezoelectric ceramictransformer. The problem related to the requisite use of a step-upvoltage transformer to first step-up voltage before driving thesingle-layered piezoelectric ceramic transformer can be therebyimproved. The fabrication process hence is facilitated, and thefabrication cost is reduced.

[0047] II. Multi-Stacked Layers Piezoelectric Ceramic Transformer

[0048] A. Testing Conditions:

[0049] 1. V(DCV): 12V±5%

[0050] 2. load: lamp length 220 mm

[0051] 3. working frequency: 73.39 KHz±2 KHz

[0052] 4. light regulation conditions: DCV 0V

[0053] 5. multi-stacked layers piezoelectric ceramic transformer ±10%:48 mm L×8 mm W×1.8 mm t

[0054] 6. static capacitance of low voltage terminal: 82.9 nf

[0055] 7. number of layers of input terminal: 18 layers

[0056] 8. testing temperature: 27±10%

[0057] B. Test Results:

[0058] Without capacitor: tube voltage (RMS) acV: 500V; tube current(AVG) mAacI: 6.86 mA;

[0059] With capacitor: tube voltage (RMS) acV: 475V; tube current (AVG)mAacI: 13.186 mA.

[0060] C. Testing Efficiency:

[0061] 1. without capacitor

[0062] tube voltage (RMS)acV×tube current (AVG)mAacI=P_out(w)

[0063] 500V×6.86 mA=3.43 W

[0064] input voltage (DCV)×input current (DCI)=P_IN

[0065] 12V×0.378 A=4.53 W

[0066] 2. with parallel capacitor tube voltage (RMS)acV×tube current(AVG)mAacI=P_out(w)

[0067] 475V×13.186 mA=6.25 W

[0068] input voltage (DCV)×input current (DCI)=P_IN

[0069] 12V×.882 A=10.58 W

[0070] As shown in the above test results, the addition of the capacitorof 0.1 uf can turn on the multi-stacked layers piezoelectric ceramictransformer.

[0071]FIG. 5 illustrates another embodiment of the invention. Asillustrated, besides parallel connecting the capacitor 42 to the inputterminal of the transformer 41, it can be also envisaged to serialconnect a capacitor 42′ between the output terminal of the transformer41 and the load (CCFL) 7 to magnify the outputted voltage and, thereby,increase the power.

[0072]FIG. 6 still illustrates another variant embodiment of theinvention. As shown, the capacitor 42 can be parallel connected to theinput terminal of the transformer 41 while being also serial connectedbetween the output terminal of the transformer 41 and the load (CCFL) 7to magnify the outputted voltage and, thereby, increase the power.

[0073] The following results compare a scheme connection in which thepiezoelectric ceramic voltage transformer is not connected to anycapacitors and connection schemes in which a capacitor is serialconnected between the output terminal and the load terminal, ordifferent capacitors are simultaneously parallel and serial connectedbetween the input terminal and the output terminal of the piezoelectricceramic voltage transformer

[0074] A. Testing Conditions:

[0075] 1. V(DCV): 12.1V±5%

[0076] 2. load: lamp length 220 mm×1 unit

[0077] 3. working frequency: 74 KHz±2 KHz

[0078] 4. light regulation conditions: DCV 0V

[0079] 5. single layer piezoelectric ceramic transformer: 42 mm L×7.4 mmW×3.7 mm t

[0080] 6. static capacitance of low voltage terminal: 185 nf

[0081] 7. number of layers of input terminal: 18 layers

[0082] 8. testing temperature: 27±10%

[0083] 9. capacitors: 100 pF, 68 nF

[0084] B. Test Results:

[0085] Without capacitor: tube current (AVG) mAacI: 7.21 mA;

[0086] With a capacitor of 100 pF serial connected to the outputterminal: tube current (AVG) mAacI: 8.25 mA.

[0087] With a capacitor of 100 pF serial connected to the outputterminal and a capacitor of 68 nF parallel connected to the inputterminal: tube current (AVG) mAacI: 10.83 mA.

[0088] From the above results, it is observed that the lamp currentoutputted can be increased via either serial connecting a capacitor tothe output terminal of the transformer, or serial connecting a firstcapacitor to the output of the transformer and simultaneously parallelconnecting a second capacitor to the input terminal of the transformer.

[0089] The invention as described above is advantageous allowing thereduction of the number of lamps 7 mounted to the LCD screen.Alternatively, with respect to the same conditions of input and load,the corresponding input voltage of the driving device can be alsoreduced. Thereby, the number of electric components can be also reduced.By further reducing the volume and number of layers of the piezoelectrictransformer, the fabrication cost is reduced, and the fabricationprocess is simpler.

[0090] Furthermore, the invention is also advantageous allowing a singlepiezoelectric ceramic transistor 4 element to be formed from thepiezoelectric ceramic transformer 41 and the capacitor 42, 42′ viasemiconductor packaging process. Alternatively, the piezoelectricceramic transformer 41 and the capacitor 42 can be connected viatraditional electric elements.

[0091] It should be apparent to those skilled in the art that the abovedescription is only illustrative of specific embodiments and examples ofthe invention. The invention should therefore cover variousmodifications and variations made to the herein-described structure andoperations of the invention, provided they fall within the scope of theinvention as defined in the following appended claims.

What is claimed is:
 1. A piezoelectric ceramic transistor, suitable foruse in piezoelectric converter device, comprising a piezoelectricceramic voltage transformer and a capacitor, the capacitor beingparallel connected to an input terminal of the piezoelectric ceramicvoltage transformer to form a bypass capacitor, thereby the power isincreased and loss due to feedback is prevented so that vibrations ofthe piezoelectric ceramic voltage transformer are compensated.
 2. Thetransistor of claim 1, wherein the piezoelectric ceramic voltagetransformer and the capacitor are connected to each other viatraditional electric element to form a piezoelectric ceramic transistorwith increased power.
 3. The transistor of claim 1, wherein thepiezoelectric ceramic voltage transformer and the capacitor areprocessed via semiconductor packaging to form a single piezoelectricceramic transistor.
 4. The transistor of claim 1, wherein thepiezoelectric ceramic transistor provides either a cold cathodefluorescent lamp (CCFL) with higher driving power or a CCFL of longerlength.
 5. A piezoelectric ceramic transistor, suitable for use inpiezoelectric converter device, comprising a piezoelectric ceramicvoltage transformer and a capacitor, the capacitor being serialconnected between an output terminal of the piezoelectric ceramicvoltage transformer and a load terminal, thereby magnifying an outputvoltage and increasing the power.
 6. A piezoelectric ceramic transistor,suitable for use in piezoelectric converter device, comprising apiezoelectric ceramic voltage transformer and at least a first and asecond capacitor, wherein the first capacitor being parallel connectedto an input terminal of the piezoelectric ceramic voltage transformerand between an output terminal of the piezoelectric ceramic voltagetransformer and a load terminal so as to form a bypass capacitor used toincrease the power and prevent a loss due to a feedback, therebycompensating vibrations of the piezoelectric ceramic voltagetransformer; while the second capacitor being serial connected betweenthe output terminal of the piezoelectric ceramic voltage transformer andthe load terminal, thereby respectively increasing an output voltage andthe power.